This NIH SBIR Phase II project will enable Dakota Technologies, Inc. (DTI) to complete development of a hollow-fiber membrane (HFM) sampling system that provides analytical quality data on volatile organic compounds (VOCs) in groundwater. The system is versatile and comprehensive; it incorporates methods and hardware for implanting the HFM samplers, methods and hardware for efficiently collecting vapors that permeate from the groundwater through the membrane, and the end step of gas chromatographic sample analysis. The basis of the measurement is VOC pervaporation from the groundwater formation into the lumen of the hollow fiber. The headspace developed in the lumen is returned to the surface via a carrier gas. Limits of detection can be adjusted over a wide range by controlling the time of trapping. Proof of concept was established through laboratory studies and a selected set of field studies. The response from one HFM sampler to another varied less than 10%. Environmentally significant contaminants such as MTBE, benzene, toluene, trichloroethylene, and perchloroethylene can be accurately measured at concentrations below 5 micrograms per liter. The Phase II activities include comprehensive laboratory studies of the permeation thermodynamics and kinetics, evaluation of alternative membrane materials and geometries, refinement of the deployment and sampling hardware, and extensive field studies. The proposed system will provide environmental consultants, regulators, and site owners vastly improved capability to fully characterize the lateral and vertical extent of VOC contamination, leading to faster and more effective remedial efforts. The ultimate beneficiaries of the research will be the citizens who rely on a supply of clean, healthy drinking water.